An underpants type disposable diaper is folded at a crotch portion so that a front body part and a back body part are overlapped, and then joined at opposite edges on both sides in a longitudinal direction, thereby to form a waist opening and a pair of right and left leg openings. Resilient and elastic members are arranged as appropriate along the waist opening and the leg openings so as to fit the diaper to the body of a wearer.
In addition, an underpants type disposable diaper has a basic layered structure with a liquid permeable face sheet, a liquid impermeable back sheet, and an absorber between the two sheets, and also has a lamination structure with an additional leak prevention sheet and the like arranged at appropriate positions.
In a particularly employed lamination structure, a larger number of sheets are arranged around the waist opening, such as a back leak prevention sheet and a reinforcing sheet for example, whereas a smaller number of sheets are arranged around the leg openings not so as to interfere with movement of the legs of a wearer.
Therefore, in many cases, an underpants type disposable diaper varies in number of laminated sheets partially at the joined sections.
Furthermore, in many cases, even an underpants type disposable diaper with no layered structure at the joined sections may vary in density of arranged resilient and elastic members around the waist opening and the leg openings, which makes differences in required adhesion force.    Patent Document 1: JP 2002-291801 A    Patent Document 2: JP 2001-178770 A